For general duplex schemes adopted in a cellular system, a Time Division Duplex (TDD) mode refers to transmission of uplink/downlink signals in the uplink and the downlink in different periods of time over the same operating frequency band, where there is a Guard Period (GP) between the uplink and the downlink; and a Frequency Division Duplex (FDD) mode refers to possible transmission of uplink/downlink signals in the uplink and the downlink concurrently over different carrier carriers in different operating frequency bands, where there is a Guard Band (GB) between the uplink and the downlink, as illustrated in FIG. 1, where T represents transmission and R represents reception.
A frame structure of a Time Division-Long Term Evolution (TD-LTE) system is somewhat complicated, as illustrated in FIG. 2, where a radio frame with a length of 10 ms includes 10 sub-frames in total including special sub-frames and normal sub-frames, and each sub-frame is 1 ms in length. The special sub-frame includes three time slots: a Downlink Pilot Time Slot (DwPTS), a GP and an Uplink Pilot Time Slot (UpPTS). The normal sub-frames include uplink sub-frames and downlink sub-frames for transmitting uplink/downlink control signaling, traffic data, etc. Particularly a radio frame can be configured with two special sub-frames (in the sub-frame #1 and the sub-frame #6 respectively) or can be configured with one special sub-frame (in the sub-frame #1). The sub-frame #0 and the sub-frame #5, and the DwPTS time slot(s) in the special sub-frame(s) are usually used for downlink transmission, the sub-frame #2 and the UpPTS time slot(s) in among the sub-frame(s) are usually used for uplink transmission, and the remaining sub-frames can be configured for uplink transmission or downlink transmission as needed.
In the TD-LIE system, the total length of three time slots DwPTS, GP and UpPTS in a special sub-frame is 1 ms, and different configuration conditions for the allocated lengths of these three time slots are supported, as depicted in Table 1, where there is a temporal length unit of Ts with Ts=1/(15000×2048) second.
TABLE 1ConfigurationNormal CPExtended CPNo.DwPTSGPUpPTSDwPTSGPUpPTS0 6592 · Ts21936 · Ts 2192 · Ts 7680 · Ts20480 · Ts 2560 · Ts119760 · Ts8768 · Ts20480 · Ts7680 · Ts221952 · Ts6576 · Ts23040 · Ts5120 · Ts324144 · Ts4384 · Ts25600 · Ts2560 · Ts426336 · Ts2192 · Ts 7680 · Ts17920 · Ts 5120 · Ts5 6592 · Ts19744 · Ts 4384 · Ts20480 · Ts5120 · Ts619760 · Ts6576 · Ts23040 · Ts2560 · Ts721952 · Ts4384 · Ts———824144 · Ts2192 · Ts———
Seven different allocation schemes of uplink/downlink sub-frames are supported in the TD-LTE system with their particular configuration parameters as depicted in Table 2, where D represents downlink transmission, U represents uplink transmission, and S represents a special sub-frame including three time slots DwPTS, GP and UpPTS.
TABLE 2Config-urationSwitchSub-frame No.No.periodicity012345678905 msDSUUUDSUUU15 msDSUUDDSUUD25 msDSUDDDSUDD310 ms DSUUUDDDDD410 ms DSUUDDDDDD510 ms DSUDDDDDDD65 msDSUUUDSUUD
The configuration of special sub-frame and the allocation scheme of uplink/downlink sub-frames above are broadcasted to all of users in a cell in System Information (SI).
As can be apparent from the description above, a change to the two frame configuration parameters above by a system information change is supported in the TD-LIE system, but this change further necessitates procedures of paging, newly fetching system information, etc., and there are several ambiguous issues before and after the change, for example, resulting in an adverse influence upon Hybrid Automatic Repeated Request (HARQ) operations and scheduling, etc. If the frame configuration were changed frequently, then the performance of the system might have been seriously degraded. Moreover the minimum frame configuration change periodicity of 640 ms supported in the TD-LTE system has not yet accommodated a dynamically changing demand for a service.
In view of this, a dynamic solution to allocation of uplink/downlink sub-frames has been proposed as follows:
In a specific period of time, there are four preset types of sub-frames including sub-frames always used for downlink transmission, sub-frames always used for uplink transmission, and sub-frames flexibly allocated for uplink or downlink transmission. The period of time is one radio frame, where the sub-frame #0 and the sub-frame #5 are always-downlink sub-frames, the sub-frame #2 and the sub-frame #7 are always-uplink sub-frames, the sub-frame #1 and the sub-frame #6 are special sub-frames (or can be always-downlink sub-frames), and the remaining sub-frames (the sub-frame #3, the sub-frame #4, the sub-frame #8 and the sub-frame #9) are sub-frames allocated flexibly for uplink or downlink transmission. The last type of sub-frames can be configured dynamically by a base station in view of a real-time traffic demand and a real-time channel condition to accommodate a dynamic change in demand for a service.
In summary, a method of configuring dynamically TDD sub-frames has been suggested in the disclosed solution of the prior art. In a real system, if different cells are preset separately with different uplink-downlink configurations, then inter-eNB or/and inter-UE interference may occur with neighboring cells, as illustrated in FIG. 3, where an L-UE represents a user equipment which belong to a low-power node. It shall be noted that the neighboring cells here may be geographically neighboring cells operating over the same frequency carrier, a illustrated in FIG. 3, or geographically overlapping or neighboring cells operating over adjacent frequency carriers, as illustrated in FIG. 4. Also the neighboring cells here may be cells deployed at the same layer (e.g., macro cells) or can be cells deployed at different layers (a macro cell, a pico cell, a femto cell, etc.) Thus the solution to configure uplink-downlink configurations dynamically suggested in the prior art has not addressed the accompanying problem of inter-eNB or/and inter-E interference, especially for inter-eNB interference, thus degrading the performance of the system.